Non-impact recording by the ink jet method is becoming popular for converting image data in the form of electrical signals into hard copies because fewer moving parts are required and less noise is produced than with impact recording. The ink jet method is also considered particularly useful because ordinary paper can be used without need for a special process, such as fixing, for recording purposes.
The ink jet method that is already in use comprises the steps of filling an airtight container with ink, applying a pressure pulse thereto, and sending the ink out of the orifice of the container in a jet for recording purposes. An ink jet recorder for the aforesaid method cannot be made compact because of its operating mechanism and requires mechanical scanning if recording has to be made with a desired image density. This latter requirement greatly reduces the recording speed. At the same time, there have been proposed techniques for remedying shortcomings inherent in the ink jet method and making high-speed recording possible.
A method using magnetic ink is an example of an alternate method. In this method magnetic ink is provided close to a magnetic electrode array to form an ink-jet state corresponding in position to a picture element by making use of a swell of the ink in the presence of a magnetic field, and jetting the magnetic ink in the presence of a static electric field. Since this method admits of electronic scanning, higher-speed recording becomes possible. The method has inherent disadvantage in constraints on the selection of ink and the coloration characteristic of the ink.
There is also known a so-called plane ink method, which comprises arranging ink in a slitlike inkholder in parallel to an electrode array, and jetting the ink in accordance with an electric field pattern formed between the electrode array and a backing electrode a supporting a recording paper. Since no minute orifice is required in this method, the problem of ink clogging can be prevented. However, a high voltage must be applied to jet the ink which makes it necessary to drive the electrode array on a time division basis to prevent a voltage leak across adjoining or neighboring electrodes. This also places restraints on the recording speed attainable with such a device.
A so-called heat bubble jet method has also been proposed for jetting ink out of an orifice by means of thermal energy. In this method, the ink is abruptly heated to cause film boiling and a pressure rise resulting from the rapid formation of bubbles within the orifice is utilized to jet the ink. The film boiling temperatures are as high as 500.degree.-600.degree. C., however, and this makes it difficult to put this method to practical use because ink properties tend to change at elevated temperatures and a protective layer on the heating resistors is deteriorated by high temperature.
As clear from the above, prior ink jet recordings methods have many unsolved problems. The problems include unsatisfactory recording speed, the requirements of special inks and complicated driving means, and thermal deterioration of the ink and the heating means.